Methods for growing single crystal silicon ingots that involve silicon feed tube inert gas control

ABSTRACT

Methods for growing single crystal silicon ingots that involve silicon feed tube inert gas control are disclosed. Ingot puller apparatus that include a flange that extends radially from a silicon funnel or from a silicon feed tube to reduce backflow of gases from the silicon feed tube into the growth chamber are also disclosed.

FIELD OF THE DISCLOSURE

The field of the disclosure relates to methods for growing singlecrystal silicon ingots that involve silicon feed tube inert gas controland to ingot puller apparatus that include a flange that extendsradially from a silicon funnel or from a silicon feed tube to reducebackflow of gases from the silicon feed tube into the growth chamber.

BACKGROUND

Continuous Czochralski (CCz) is well suited to form 300 mm or 200 mmdiameter single crystal silicon ingots. Continuous Czochralski methodsinvolve forming a single crystal silicon ingot from a melt of siliconwhile continuously or intermittently adding solid polycrystallinesilicon to the melt to replenish the melt while the ingot is grown. Themethods may involve forming multiple ingots from the same melt while thehot zone remains at temperature (i.e., with a melt continuously beingpresent in the crucible assembly while the plurality of ingots isgrown).

Solid-state silicon is added to the melt through a silicon feed tubethat directs the silicon to the melt. Periodically, the silicon feedtube becomes occluded and silicon cannot pass through the tube. Cloggingof the feed tube causes the ingot production run to be stopped and theingot puller apparatus to be taken out of service which reducesthroughput and increases cost. An inert gas such as argon may be passedthrough the tube to reduce clogging. However, the flow of inert gas cancause inert gas bubbles (e.g., argon bubbles) to form in the melt whichimpacts the void count in the resulting ingot and sliced wafers.Customers expect that wafers grown by continuous Czochralski have thesame relatively low void count as wafers grown by standard batchCzochralski.

A need exists for ingot puller apparatus and methods for forming aningot that reduce occlusion of the silicon feed tube and that do notresult in formation of excessive inert gas bubbles in the melt.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the disclosure, which aredescribed and/or claimed below. This discussion is believed to behelpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

SUMMARY

One aspect of the present disclosure is directed to a method for growinga single crystal silicon ingot in a continuous Czochralski process in aningot puller apparatus. The ingot puller apparatus includes a housingdefining a growth chamber, a crucible assembly disposed in the growthchamber, and a silicon feed tube for adding solid silicon to thecrucible assembly. A melt of silicon is formed in a crucible assembly.Heat is applied to the melt in a stabilization phase. An inert gas isintroduced into the silicon feed tube at a first inert gas feed rateduring the stabilization phase. A surface of the melt is contacted witha seed crystal. A single crystal silicon ingot is withdrawn from themelt in an ingot growth phase. The inert gas is introduced into thesilicon feed tube at a second inert gas feed rate during the ingotgrowth phase. The first inert gas feed rate is greater than the secondinert gas feed rate.

Another aspect of the present disclosure is directed to a method forgrowing a single crystal silicon ingot in a continuous Czochralskiprocess in an ingot puller apparatus. The ingot puller apparatusincludes a housing defining a growth chamber, a crucible assemblydisposed in the growth chamber, and a silicon feed tube for adding solidsilicon to the crucible assembly. A melt of silicon is formed in acrucible assembly. Heat is applied to the melt in a stabilization phase.An inert gas is introduced into the silicon feed tube at a first inertgas feed rate during the stabilization phase. The first inert gas feedrate is between 2.5 and 3.5 slpm. A surface of the melt is contactedwith a seed crystal. A single crystal silicon ingot is withdrawn fromthe melt in an ingot growth phase. The inert gas is introduced into thesilicon feed tube at a second inert gas feed rate during the ingotgrowth phase. The second inert gas feed rate is between 2.5 and 3.5slpm.

A further aspect of the present disclosure is directed to an ingotpuller apparatus for manufacturing a single crystal silicon ingot. Theingot puller apparatus includes a crucible assembly for holding asilicon melt. A crystal puller housing defines a growth chamber forpulling a silicon ingot from the melt. The crucible assembly is disposedwithin the growth chamber. The ingot puller apparatus includes a siliconfeed tube for adding solid silicon to the crucible assembly. A funnel atleast partially extends into the silicon feed tube. The funnel andsilicon feed tube are separated by a gap. A flange extends radially fromthe funnel or from the silicon feed tube. The flange extends across atleast a portion of the gap to reduce backflow of gases from the siliconfeed tube into the growth chamber.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Further features mayalso be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of an example ingot puller apparatus with asilicon charge disposed in the crucible assembly;

FIG. 2 is a is a cross-section of the ingot puller apparatus aftermelt-down and during the stabilization phase;

FIG. 3 is a cross-section of the ingot puller apparatus with the siliconseed crystal lowered to contact the melt to begin the ingot growthphase;

FIG. 4 is a is a cross-section of the ingot puller apparatus during theingot growth phase;

FIG. 5 is a perspective view of a silicon feed system for adding siliconto the crucible assembly;

FIG. 6 is a detailed cross-section of the ingot puller apparatus showingthe silicon feed tube;

FIG. 7 is a detailed cross-section of an embodiment of an ingot pullerapparatus showing a flange that extends from the funnel;

FIG. 8 is a detailed cross-section of another embodiment of an ingotpuller apparatus showing a flange that extends from the lower end of thefunnel;

FIG. 9 is a simulation of the mass fraction of SiO in the silicon feedtube during the ingot growth phase;

FIG. 10 is a simulation of the mass fraction of SiO in the silicon feedtube during the stabilization phase; and

FIG. 11 shows box plots of the defect counts for wafers grown with anargon gas flow rate through the silicon feed tube of 12 slpm (Crystal 1and Crystal 2) and for wafers grown with an argon gas flow rate throughthe silicon feed tube of 3 slpm (Crystal 3).

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Provisions of the present disclosure relate to methods for growing asingle crystal silicon ingot in a continuous Czochralski process in aningot puller apparatus and to ingot puller apparatus having a flangethat extends across a portion of a gap between the funnel and siliconfeed tube. The methods and apparatus may reduce downstream clogging ofthe silicon feed tube.

An example ingot puller apparatus (or more simply “ingot puller”) isindicated generally at “100” in FIG. 1 . The ingot puller apparatus 100includes a crucible assembly 102 for holding a melt 104 (FIG. 2 ) ofsemiconductor or solar-grade material silicon. The crucible assembly 102is supported by a susceptor 106. The ingot puller apparatus 100 includesa crystal puller housing 108 that defines a growth chamber 152 forpulling a silicon ingot 113 (FIG. 4 ) from the melt 104 along a pullaxis A.

The crucible assembly 102 has a sidewall 131 (FIG. 1 ) and one or morefluid barriers 121, 130 or “weirs” that separate the melt into differentmelt zones. In the illustrated embodiment, the crucible assembly 102includes a first weir 121. The first weir 121 and sidewall 131 define anouter melt zone 143 (FIG. 2 ) of the silicon melt 104 and the crucibleassembly 102. The crucible assembly 102 includes a second weir 130radially inward to the first weir 121 which defines an inner melt zone127 of the silicon melt 104 and crucible assembly 102. The inner meltzone 127 is the growth region from which the single crystal siliconingot 113 (FIG. 4 ) is grown. The first weir 121 and the second weir 130define a middle melt zone 132 of the crucible assembly 102 and siliconmelt 104 in which the melt 104 may stabilize as it moves toward theinner melt zone 127. The first and second weirs 121, 130 each have atleast one opening formed therein to permit molten silicon to flowradially inward towards the inner melt zone 127.

In the illustrated embodiment, the first weir 121, second weir 130, andsidewall 131 each have a generally annular shape. The first weir 121,second weir 130, and sidewall 131 may be part of three nested crucibleswhich are joined at the bottom or floor 129 of the crucible assembly 102(i.e., the first and second weirs 121, 130 are the sidewalls of twocrucibles nested within a larger crucible). The crucible assemblyconfiguration depicted in FIGS. 1-4 is exemplary. In other embodiments,the crucible assembly 102 has a single layer floor (i.e., does not havenested crucibles) with the weirs extending upward from the floor 129.Optionally, the floor 129 may be flat rather than curved and/or theweirs 121, 130 and/or sidewall 131 may be straight-sided. Further, whilethe illustrated crucible assembly 102 is shown with two weirs, in otherembodiments the crucible assembly may have a single weir or even noweirs.

The susceptor 106 is supported by a shaft 105. The susceptor 106,crucible assembly 102, shaft 105, and ingot 113 (FIG. 4 ) have a commonlongitudinal axis or “pull axis” A.

A pulling mechanism 114 is provided within the ingot puller apparatus100 for growing and pulling an ingot 113 (FIG. 4 ) from the melt 104.Pulling mechanism 114 includes a pulling cable 118, a seed holder orchuck 120 coupled to one end of the pulling cable 118, and a seedcrystal 122 coupled to the seed holder or chuck 120 for initiatingcrystal growth. One end of the pulling cable 118 is connected to apulley (not shown) or a drum (not shown), or any other suitable type oflifting mechanism, for example, a shaft, and the other end is connectedto the chuck 120 that holds the seed crystal 122. In operation, the seedcrystal 122 is lowered to contact the surface of the melt 104 (FIG. 3 ).The pulling mechanism 114 is operated to cause the seed crystal 122 torise. This causes a single crystal ingot 113 (FIG. 4 ) to be pulled fromthe melt 104.

During heating and crystal pulling, a crucible drive unit 107 (e.g., amotor) rotates the crucible assembly 102 and susceptor 106. A liftmechanism 112 raises and lowers the crucible assembly 102 along the pullaxis A during the growth process. For example, the crucible assembly 102may be at a lowest position (near the bottom heater 126) in which acharge of solid-phase polycrystalline silicon 133 previously added tothe crucible assembly 102 is melted. Crystal growth commences bycontacting the melt 104 (FIG. 2 ) with the seed crystal 122 and liftingthe seed crystal 122 by the pulling mechanism 114.

A crystal drive unit (not shown) may also rotate the pulling cable 118and ingot 113 (FIG. 4 ) in a direction opposite the direction in whichthe crucible drive unit 107 rotates the crucible assembly 102 (e.g.,counter-rotation). In embodiments using iso-rotation, the crystal driveunit may rotate the pulling cable 118 in the same direction in whichcrucible drive unit 107 rotates the crucible assembly 102.

According to the Czochralski single crystal growth process, a quantityof solid-phase silicon 133 (FIG. 1 ) such as polycrystalline silicon, orpolysilicon, is charged to the crucible assembly 102. The semiconductoror solar-grade material that is introduced into the crucible assembly102 is melted by heat provided from one or more heating elements. Thesize of the solid-phase silicon charge 133 may correspond to the desiredsize of the melt when ingot growth commences or, as in otherembodiments, a smaller charge is used and additional silicon is added bya silicon feed system 200 to form the initial volume of melt presentduring initiation of ingot growth.

The ingot puller apparatus 100 includes bottom insulation 110 and sideinsulation 124 to retain heat in the puller apparatus 100. In theillustrated embodiment, the ingot puller apparatus 100 includes a bottomheater 126 disposed below the crucible floor 129. The crucible assembly102 may be moved to be in relatively close proximity to the bottomheater 126 to melt the polycrystalline charged to the crucible assembly102.

The silicon melt 104 is stabilized in a stabilization phase previous tothe ingot grown phase. In some embodiments, the stabilization phaseincludes at least the period between formation of the melt (aftermeltdown) and contact of the surface of the melt with the seed crystal.In some embodiments, the stabilization phase also includes the period atwhich silicon is melted down in the crucible assembly 102 (i.e.,meltdown of the initial charge and any other silicon added to form theinitial melt).

To form the ingot, after the melt is stabilized in the stabilizationphase, the seed crystal 122 is contacted with the surface 111 of themelt 104 as shown in FIG. 3 . The pulling mechanism 114 is operated topull the seed crystal 122 from the melt 104 in an ingot growth phase.Referring now to FIG. 4 , the ingot 113 includes a crown portion 142 inwhich the ingot transitions and tapers outward from the seed crystal 122to reach a target diameter. The ingot 113 includes a constant diameterportion 145 or cylindrical “main body” of the crystal which is grown byincreasing the pull rate. The main body 145 of the ingot 113 has arelatively constant diameter. The ingot 113 includes a tail or end-cone(not shown) in which the ingot tapers in diameter after the main body145. When the diameter becomes small enough, the ingot 113 is thenseparated from the melt 104.

The ingot puller apparatus 100 includes a side heater 135 and asusceptor 106 that encircles the crucible assembly 102 to maintain thetemperature of the melt 104 during crystal growth. The side heater 135is disposed radially outward to the crucible sidewall 131 as thecrucible assembly 102 travels up and down the pull axis A. The sideheater 135 and bottom heater 126 may be any type of heater that allowsthe side heater 135 and bottom heater 126 to operate as describedherein. In some embodiments, the heaters 135, 126 are resistanceheaters. The side heater 135 and bottom heater 126 may be controlled bya control system (not shown) so that the temperature of the melt 104 iscontrolled throughout the pulling process.

The ingot puller apparatus 100 may include a heat shield 151. The heatshield 151 may shroud the ingot 113 and may be disposed within thecrucible assembly 102 during crystal growth (FIG. 4 ). The ingot pullerapparatus 100 may include an inert gas system to introduce and withdrawan inert gas such as argon from the growth chamber 152.

The ingot puller apparatus 100 also includes a silicon feed system 200for introducing solid-state silicon (e.g., polycrystalline silicon orsingle crystal silicon scrap material) into the crucible assembly 102and, in particular, the outer melt zone 143. The solid-state silicon maybe added continuously during ingot growth to maintain a substantiallyconstant melt elevation level and volume during growth of the ingot 113or may be added intermittently between crystals. The solid silicon thatis fed to the crucible assembly 102 by the silicon feed system 200 maybe, for example, granular, chunk, chip, or a combination of thereof. Thesilicon feed system 200 adds or meters solid-state silicon into andthrough a silicon feed tube 214. Referring now to FIG. 5 , an examplesilicon feed system 200 of the present disclosure is shown. The siliconfeed system 200 includes a canister 204 for holding solid-state silicon.The canister 204 includes a removable lid 207 for sealing the canister204. The canister 204 also includes a funnel portion 211 which directssilicon to a feed tray 260 disposed below the canister 204.

To move silicon from the canister 204 to the feed tube 214, the siliconfeed system 200 includes a feed tray 260 disposed below the canister 204that extends between the canister 204 and a port 229 (FIG. 6 ) thatextends through the ingot puller housing 108. The feed tray 260 isdisposed above and is connected to a vibrator 262. Powering the vibrator262 causes the feed tray 260 to vibrate which conveys silicon from thecanister 204 and across the feed tray 260. Silicon is discharged fromthe feed tray 260 and into a port opening 232 (FIG. 6 ) (e.g., through atube or chute (not shown) disposed below the feed tray 260). Siliconfalls through the port opening 232 and into a funnel 222 disposed belowthe port 229. From the funnel 222 the silicon falls into the silicontube 214. Silicon may be added to maintain a constant position of themelt surface and may be controlled by the power supplied to the vibrator262.

The port 229 and silicon feed tube 214 are sealed with the canister 204to isolate the growth chamber 152 (FIG. 1 ) of the ingot pullerapparatus 100 from the surrounding ambient. For example, the siliconfeed system 200 may include an outer housing 252 with other componentsof the feed system being disposed within the outer housing 252. An inertgas such as argon may be introduced from an inert gas feed vessel 255into the outer housing 252. The inert gas passes through the portopening 232 (FIG. 6 ) and into the silicon feed tube 214.

The silicon feed system 200 is exemplary and any feed system thatenables silicon to be introduced into the crucible assembly 102 may beused. For example, other feed systems may include liquid feed systems.

Referring now to FIG. 6 , the tube 214 includes a receiving portion 225and a main portion 227 disposed below the receiving portion 225. Thefunnel 222 is partially disposed within the receiving portion 225 of thesilicon feed tube 214. The receiving portion 225 of the tube includes aconstant diameter segment 231 and a tapering segment 223 that tapers tothe main portion 227 of the tube 214. The main portion 227 of the tube214 has an angled segment 243 (i.e., a segment that extends radiallyinward in the puller apparatus 100) and a terminal segment 245 thatextends from the angled segment 243. The silicon tube 214 includes anupper end 221 and a lower end 249.

In accordance with embodiments of the present disclosure, the amount ofinert gas that is introduced into the port 229 and that travels throughthe funnel 222 and the silicon tube 214 is regulated to reducedownstream clogging of the tube 214. For example, different flow ratesmay be used during the stabilization phase and the ingot growth phase.During the stabilization phase, the inert gas is introduced into thesilicon feed tube at a first inert gas feed rate. During the ingotgrowth phase, the inert gas is introduced into the silicon feed tube ata second inert gas feed rate. The first inert gas feed rate is greaterthan the second inert gas feed rate. For example, the ratio of the firstinert gas feed rate to the second inert gas feed rate may be at least5:4, at least 4:3, at least 3:2 or at least 2:1. In some embodiments,the first inert gas feed rate is greater than 3 slpm and the secondinert gas feed rate is from 1 slpm to 3 slpm. For example and inaccordance with some particular embodiments, the first inert gas feedrate and the second inert gas feed rate are each between 2.5 and 3.5slpm.

It should be noted that the inert gas feed rates and ratios describedabove may apply to the entire respective stabilization phase or inertgas phase or, as in some embodiments, at least 75% of the respectivephase, or at least 85%, at least 95%, or at least 99% of the respectivephase.

In some embodiments, there may be a gap 233 (e.g. open gap as shown inFIG. 6 ) between the funnel 222 and the silicon feed tube 214. Someinert gas may exit the gap 233 instead of proceeding through the lengthof the tube 214. The flow rates and/or ratios of flow rates describedherein may refer to the amount of gas introduced through the portopening 232 (i.e., upstream of any gases passing through gap 223).

Referring now to FIGS. 7-8 , in some embodiments, the silicon feed tube214 and/or funnel 222 may be modified relative to conventional tubes andfunnels. The feed tube 214 and/or funnel may reduce clogging of the tube214 relative to conventional tubes and funnels. The silicon feed tube214 and/or funnel 222 described below may be used in combination withthe inert gas flow rates and ratios described above or the flow ratesand ratios may be used without the modified tube 214 and funnel 222 andthe modified tube 214 and funnel 222 may be used with different inertgas flow rates and ratios.

As shown in FIG. 7 , the funnel 222 at least partially extends into thesilicon feed tube 214. The funnel 222 includes a tapering portion 237that is disposed below the opening 232 of the port 229. The funnel 222has a chute portion 240 that partially extends into the silicon feedtube 214. The funnel 222 has an upper end 212 and a lower end 215 withthe lower end 215 being disposed within the silicon feed tube 214. Thesilicon feed tube 214 includes a receiving portion 225 in which thechute portion 240 of the funnel 222 is partially disposed. The receivingportion 225 has a diameter larger than the main portion 227 of the tube214.

The funnel 222 and silicon feed tube 214 are separated by a gap 219. Theingot puller apparatus 100 includes a flange 230 that extends radiallyfrom the funnel 222. The flange 230 extends across at least a portion ofthe gap 219 (e.g., the entire gap 219 as shown in FIG. 7 or partiallyacross the gap 219 as shown in FIG. 8 ) to reduce backflow of gases fromthe silicon feed tube 214 into the growth chamber 152 (FIG. 1 ).

In the embodiment illustrated in FIG. 7 , the flange 230 extends fromthe funnel 222 and is disposed above the silicon feed tube 214 (i.e.,directly above). The flange 230 contacts an upper end 221 of the feedtube 214. In the embodiment illustrated in FIG. 8 , the flange 230extends from the funnel 222 and is disposed within the silicon feed tube214 (e.g., the receiving portion 225 of the tube 214). The flange 230only partially extends across a portion of the gap 219. In theillustrated embodiment, the flange 230 extends from the lower end 215 ofthe funnel 222. In some embodiments, the ingot puller apparatus of FIG.7 is modified to also include the flange shown in FIG. 8 (i.e., theingot puller apparatus 100 includes both flanges). The flange 230 ofFIG. 7 and the flange 230 of FIG. 8 may extend from either the feed tube214 or funnel 222.

The flange 230 may be made of quartz (e.g., devitrified quartz) orsilicon carbide. The flange 230 may be a separate ring that is connectedto the tube 214 or funnel 222 or may be integral with the tube 214 orfunnel 222 (e.g., as one manufactured part).

It should be noted that in embodiments in which the ingot pullerapparatus has been modified from conventional apparatus, generally anyingot puller apparatus that includes a flange that extends across aportion of the gap to reduce backflow of gases from the silicon feedtube into the growth chamber may be used unless stated otherwise. Theingot puller apparatus shown in FIGS. 7-8 are example apparatus andother arrangements of silicon tubes, funnels and/or flanges may be used.While the silicon feed tube 214 has been described with reference toaddition of silicon, the tube 214 may be used to add dopant or quartzcullets to the silicon melt.

Compared to conventional methods, the methods of the present disclosurefor growing a single crystal silicon ingot in a continuous Czochralskiprocess have several advantages. Without being bound by any particulartheory, it is believed that clogging of the feed tube is caused bychemical vapor deposition of silicon oxides (SiO_(x)) on the innersurface of the feed tube. The silicon oxide originates from the siliconmelt from which it evaporates and rises inside the feeding tube due tobuoyancy forces. Once inside the feed tube, silicon oxide rises andencounters lower temperature regions causing deposition of metallicsilicon and silicon dioxide by the formula:2SiO→SiO₂+Si  (1).It is believed that by reducing the SiO concentration to 1 wt % or less,clogging in the feed tube may be prevented. During the stabilizationphase, it is more difficult to suppress the concentration of SiO due tothe higher temperatures used to keep the silicon molten. Clogging of thefeed tube causes the ingot production run to be stopped and the ingotpuller apparatus to be taken out of service. By controlling the flowrate of inert gas that passes through the silicon feed tube such thatthe flow rate is higher during the stabilization phase and relativelylower during the ingot growth phase, the flow rate is increased duringhigh temperature stabilization phase (stabilization contributing to moreclogging than the ingot growth phase due to its higher temperature) andthe flow rate is decreased during ingot growth which reduces inert gasbubbles which cause defects in the ingot.

In embodiments in which the ingot puller apparatus includes a flangethat extends radially from the funnel or from the silicon feed tube andextends across at least a portion of a gap between the funnel and thefeed tube, the flange reduces backflow of gases from the silicon feedtube into the growth chamber.

In embodiments in which the inert gas feed rate is near 3 slpm (e.g.,2.5 slpm to 3.5 slpm) in both the stabilization phase and ingot growthphase, the concentration of SiO in the silicon feed tube may bemaintained at 1.0 wt % at all stages of the ingot growth process whichis believed to be the threshold at which the CVD reaction occurs.

EXAMPLES

The processes of the present disclosure are further illustrated by thefollowing Examples. These Examples should not be viewed in a limitingsense.

Example 1: SiO Mass Fraction in the Silicon Feed Tube During theStabilization Phase and the Ingot Growth Phase

FIG. 9 is a simulation of the mass fraction of silicon oxide (SiO)during the ingot growth phase and FIG. 10 is a simulation of the massfraction of SiO during the stabilization phase. During the ingot growthphase (FIG. 9 ), the flow of SiO into the silicon feed tube was 0.0132g/s. During the stabilization phase (FIG. 10 ), the flow of SiO into thesilicon feed tube was 0.0142 g/s. As can be seen from the Figures, thestabilization phase included a higher mass fraction of SiO compared tothe ingot growth phase. As shown in FIG. 10 , the concentration of SiOwas higher at the junction between the angled segment of the tube andthe terminal segment of the tube (i.e., at the lower bend in the tube)where clogging most often occurs. During stabilization, the temperatureat this junction is between 900° C. and 1000° C. which is within thecritical temperature range for the CVD reaction.

Example 2: Reduction in Wafer Defects by Reducing Inert Gas Flow Rate

Three single crystal silicon ingots were prepared by continuousCzochralski with an in ingot puller apparatus shown in FIG. 1 . Crystal1 and Crystal 2 were grown using an argon flow rate of 12 slpm throughthe silicon feed tube 214 and Crystal 3 was grown using a flow rate of 3slpm. The count of the defects on the surface of wafers sliced from theingots was determined for each ingot and is shown in FIG. 11 . As shownin FIG. 11 , the ingot grown with an argon flow rate of 3 slpm throughthe silicon feed tube 214 had significantly less defects.

As used herein, the terms “about,” “substantially,” “essentially” and“approximately” when used in conjunction with ranges of dimensions,concentrations, temperatures or other physical or chemical properties orcharacteristics is meant to cover variations that may exist in the upperand/or lower limits of the ranges of the properties or characteristics,including, for example, variations resulting from rounding, measurementmethodology or other statistical variation.

When introducing elements of the present disclosure or the embodiment(s)thereof, the articles “a,” “an,” “the,” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” “containing,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. The use of terms indicating a particular orientation (e.g.,“top,” “bottom,” “side,” etc.) is for convenience of description anddoes not require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing[s] shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A method for growing a single crystal siliconingot in a continuous Czochralski process in an ingot puller apparatus,the ingot puller apparatus comprising a housing defining a growthchamber, a crucible assembly disposed in the growth chamber, a siliconfeed tube for adding solid silicon to the crucible assembly, the methodcomprising: forming a melt of silicon in a crucible assembly; applyingheat to the melt in a stabilization phase; introducing an inert gas intothe silicon feed tube at a first inert gas feed rate during thestabilization phase, inert gas being passing through the silicon feedtube and into the growth chamber during the stabilization phase;contacting a surface of the melt with a seed crystal; withdrawing asingle crystal silicon ingot from the melt in an ingot growth phase; andintroducing the inert gas into the silicon feed tube at a second inertgas feed rate during the ingot growth phase, the first inert gas feedrate being greater than the second inert gas feed rate, inert gas beingpassing through the silicon feed tube and into the growth chamber duringthe ingot growth phase.
 2. The method as set forth in claim 1 wherein aratio of the first inert gas feed rate to the second inert gas feed rateis at least 5:4.
 3. The method as set forth in claim 1 wherein the firstinert gas feed rate is greater than 3 slpm and the second inert gas feedrate is from 1 slpm to 3 slpm.
 4. The method as set forth in claim 1wherein the inert gas is argon.
 5. The method as set forth in claim 1wherein the silicon feed tube is disposed below a funnel, the inert gasflowing through the funnel into the silicon feed tube.
 6. The method asset forth in claim 5 wherein the ingot puller apparatus comprises asilicon feed system comprising a feed tray, the silicon feed systembeing sealed, the inert gas being introduced into the silicon feedsystem from an inert gas feed vessel.
 7. The method as set forth inclaim 1 wherein the crucible assembly comprises a weir and a sidewallthat define an outer melt zone between the weir and the sidewall, themethod comprising introducing silicon to the silicon feed tube whilewithdrawing a single crystal silicon ingot from the melt, siliconpassing through the silicon feed tube and entering the outer melt zone.8. The method as set forth in claim 1 wherein the stabilization phaseextends at least between formation of the melt and contacting thesurface of the melt with the seed crystal.
 9. The method as set forth inclaim 8 wherein the stabilization phase comprises meltdown of silicondisposed in the crucible assembly.
 10. A method for growing a singlecrystal silicon ingot in a continuous Czochralski process in an ingotpuller apparatus, the ingot puller apparatus comprising a housingdefining a growth chamber, a crucible assembly disposed in the growthchamber, a silicon feed tube for adding solid silicon to the crucibleassembly, the method comprising: forming a melt of silicon in a crucibleassembly; applying heat to the melt in a stabilization phase;introducing an inert gas into the silicon feed tube at a first inert gasfeed rate during the stabilization phase, the first inert gas feed ratebeing between 2.5 and 3.5 slpm, inert gas being passing through thesilicon feed tube and into the growth chamber during the stabilizationphase; contacting a surface of the melt with a seed crystal; withdrawinga single crystal silicon ingot from the melt in an ingot growth phase;and introducing the inert gas into the silicon feed tube at a secondinert gas feed rate during the ingot growth phase, the second inert gasfeed rate being between 2.5 and 3.5 slpm, inert gas passing through thesilicon feed tube and into the growth chamber during the ingot growthphase.
 11. The method as set forth in claim 10 wherein the inert gas isargon.
 12. The method as set forth in claim 10 wherein the first andsecond inert gas feed rates are each about 3.0 slpm.
 13. The method asset forth in claim 1 wherein a ratio of the first inert gas feed rate tothe second inert gas feed rate is at least 4:3.
 14. The method as setforth in claim 1 wherein a ratio of the first inert gas feed rate to thesecond inert gas feed rate is at least 2:1.